Over 139 million people, across a broad spectrum of industries in the US, work under threat of occupational exposure to hazardous chemicals. Hazardous chemical exposure in the US work place has been estimated to be responsible for 860,000 occupational illnesses and 60,000 deaths annually, with a total economic cost of $171 billion. The negative health impact and financial burden associated with occupational exposure to hazardous chemicals has prompted federal regulatory agencies to mandate the use of personal protective equipment and to set limits on acceptable exposure levels. This proposal is focused on the health of 360,000 workers in US mines, who are documented to be at increased risk of exposure to NO2 due to recent changes in diesel engine technology. While federal regulation (30 CFR 70.1900) requires that NO2 concentrations in mines be maintained below specified levels, existing technologies for measurement of NO2 concentrations are not optimal for mines because they are cumbersome, prohibitively expensive, require on-site at- elevation calibrations, and/or are prone to false positives. In this proposal, we seek to initiate the development of a liquid crystal (LC)-based technology suitable for reporting hazardous concentrations of gases in a broad spectrum of US work environments. While the technology is potentially applicable for measurement of personal exposure to a range of toxic gases in the work place, NO2 was selected as an initial target for the technology because exposure to NO2 is a key risk for mine workers and because it is prototypical of a broad class of occupational chemical hazards. This 2-year, NIOSH R21 proposal aims to realize a LC- based detection technology that will offer a small and inexpensive direct read instrument (DRI) to report NO2 concentration in real-time. DRIs based on this technology possess the potential to overcome the barriers (size, complexity, sensitivity, cost) that currently prevent existing technologies from being used for personal exposure assessment. The innovation behind the proposed DRI centers around the use of LCs supported on chemically functionalized surfaces that, upon exposure to targeted analytes, undergo an ordering transition. In preliminary studies using non-optimized system components, Platypus Technologies LLC has successfully employed the LC technology to detect 1 ppm of NO2 in less than 10 minutes, with a limit of detection of 0.01 ppm. Building from these compelling preliminary data, the goal of research in this proposal is to develop a DRI to report NO2 concentrations between 0.1 to 10 ppm. The approach will leverage Platypus's close ties with industry leaders in occupational exposure assessment (SKC, Inc, PA and Mine Safety Co, PA) and academic leaders in LC sensing and microtechnologies (University of Wisconsin- Madison and University of Alabama-Huntsville). Successful completion of this project will provide an LC-based DRI for NO2 exposure assessment that will enable every mine worker to continuously monitor their exposure to NO2 thereby increasing the awareness of risks and promoting a healthier and safer workplace. In the long term, LC-based DRI's have the potential to be a broadly applicable platform technology, offering multi-analyte monitoring in the workplace.